Several common diseases such as heart failure and type 1 diabetes are characterized by cellular degeneration in the affected organ. While a variety of drugs have been developed that treat the symptoms of such diseases, in many cases these drugs do not correct the underlying cellular degeneration causing the diseases, but rather merely ameliorate some of the symptoms of the disease. A theoretically more preferable method to treat the disease is to replace the degenerating or dead cells with healthy cells, e.g., by organ transplantation. Although successful in many cases, organ transplantation remains a complex process replete with both clinical and practical problems such as risk of immune system-mediated rejection and lack of donor organs.